The present invention relates in general to sheet-fed, multi-color, rotary printing machines including a plurality of printing units provided with sheet-turning devices therebetween. In particular, this invention relates to a control system for printing machines of this kind for changing over a first or face printing to the first and second or back-up printing.
In the DD Pat. No. 94 400, a control system for multi-color printing machines of this kind is described, which consists of a plurality of interconnected control systems assigned to respective printing units of the machine. During the first or face printing mode of operation, the control device produces a synchronization of the starting command with each rotation and with the phase in the rotation at which the start or introductory command in the corresponding unit is to be executed. In the first printing mode of operation, the assignment of a definite rotation and of a definite phase to corresponding initiating commands is constant and, depending on the geometry of the printing machine. The initiating commands activate an interrogating stage which is responsive to the signal exchange in the assigned control device for the printing unit and controls groups of functional elements in this printing unit.
In the first- and second (back-up) printing mode of operation, in which the sheets are turned over so that it is their trailing edge which is first transferred to the next printing unit and not their leading edge, and the aforementioned constant assignment or coordination of the sheets relative to the angular positions of the cylinders is no longer present. Instead, there is a constant phase shift in the movement of the sheets. Moreover, there is also a variable phase shift resulting from the different formats of the processed sheets. In order to compensate for these phase shifts, the prior-art control device includes an auxiliary control device cooperating with a timing pulse generator. The auxiliary control device is activated via a switching device and via the timing device, which in turn is responsive to the changeover from the first printing to the first and second printing mode of operation.
The disadvantage of this prior-art arrangement is the fact that it is necessary to control auxiliary control device by means of the timing pulse generator, which in turn is dependent on the changeover from the first printing to the first and second printing, and is arranged on a printing unit after its sheet-turning device. This auxiliary control device is arranged outside a central control station, in order to ensure the desired adjustment.